Radiative heat switch



Jan. 5, 1965 N. E. HAGER, JR 3,163,392

RADIATIVE HEAT SWITCH Filed Jan. 25, 1960 A B l 'l lg il A INVENTOR NATHANIEL E- HAGER,JR-

ATTORNEY 6 DEGREES) United States Patent 3,163,892 RADIATIVE HEAT W1TCH Nathaniel E. Huger, Jan, Manheim Township, Lancaster County, Pa, assignor to Armstrong Cori; Company, Lancaster, Pin, a corporation of Pennsylvania Filed lan. 25, 1960, Ser. No. 4,364

2 Claims. (Cl. 20-62) This invention relates broadly to a heat switch which is adapted to regulate heat flow and more particularly relates to a radiative heat switch which is adapted to regulate infrared and/or solar radiation.

In modern buildings, the utilization of heat from solar radiation is often inhibited by the amount of insulation required for economic heating and/or air conditioning. In addition, the well insulated home of today is not capable of fully utilizing the cooler conditions which sometimes prevail outside, during the evening and early morning hours, as a method of cooling during warm weather.

It is an object of this invention to provide a radiative heat switch which in turn will provide a selective means by which heat flow, resulting from long wave length infrared radiative exchange between members opaque to this radiation,'may be either increased of decreased.

Another object of this invention is to provide a heat switch for regulating the transmission of short wave length or visible radiation through glass or other trans parent walls. I Y

These and other objects will become more evident as the description proceeds when taken in conjunction with the drawings wherein:

FIGURE 1 is a perspective view of a panel which is utilized in the heat switch of this invention;

FIGURE 2 is a sectional view of the panel illustrated in FIGURE 1 showing the panel positioned between two parallel surfaces and showing the louvers in a position.

whereby heat flow through the switch is maximized;

FIGURE 3 is a sectional view of the panel illustrated in FIGURE 1 showing the panel positioned between two parallel surfaces and showing the louvers in a position whereby heat flow through the switch is minimized; and

FIGURE 4 is a graph illustrating effective thermal conductivities obtained with a heat switch produced in accordance with this invention.

In accordance with this invention, an effective radiative heat switch is provided bytwo elements having substantially parallel outer surfaces, a frame positioned between said parallel surfaces, a series of louvers mounted on axes which fall in a plane parallel with and between said parallel surfaces and means for adjusting said louvers between a position which is substantially parallel to said surfaces and a position which is substantially perpendicular to said surfaces, said louvers when in a position substantially parallel to said surfaces forming a substantially continuous surface and defining, with the other elements of said enclosed panel, two separate compartments. The elements forming the outer surfaces of said enclosed panel are preferably formed from a material having a relatively high emissivity to infrared radiation while the individual louvers are formed of a material which is opaque and which has high reflectivity and low emissivity with respect to radiant heat. The louvers may be formed from certain metals, such as aluminum and some forms of stainless steel, or they may be formed from numerous types of base materials carrying very thin films or deposits of metals upon the base material such that the combination if film or deposit and base provides a highly reflective, low emissivity surface having high opacity to infrared and visible radiation.

In order to more fully illustrate this invention, reference is now made to the drawings wherein FIGURE 1 "ice ponent of the radiative heat switch of this invention.

I Four elements, 5, 6, 7, and 8, respectively, form the frame of the panel. Rods 9 are arranged as shown, extending between frame members 5 and 6, the ends'of the individual rods passing through appropriate drilled holes in said frame elements. Each rod in turn is substantially parallel to frame elements 7 and 8. Attached to each rod 9 are individual louvers 10.

FIGURES 2 and 3 are sectional views illustrating a heat switch in which the panel of FIGURE 1 is combined with two elements 15 and 16 having parallel sur faces 11 and 12 respectively. The rods 9 are spaced from each other such that the louvers 10, when positioned as shown in FEGURE 3, form a substantially continuous reflective surface and define, with the parallel 11 /2" square using A" plywood strips having a width of 1%". Rods 9 were fashioned from drill rod material and louvers formed from 0.004" aluminum sheet material were fastened to each of the rods with Duco cement. The individual louvers 10 were 1" in width. Eleven drill rods were used to support the louvers and these were spaced, starting /2" in from element 8, at 1" intervals along elements 5 and 6. V

The panel thus formed was placed beneath a 12 X 12" x 4" aluminum hot plate, element 15, heated by electrical resistant elements throughout the plate and on top of a cellular glass slab, element 16, having dimensions 12" x 12" x 1" thick which in turn rested on top of a A thick 12 x 12" square aluminum cold plate. The surface of the aluminum hot plate which formed the upper parallel surface 11 of the heat switch was lacquered black and had an emissivity factor of approximately 0.92.

The cellular glass panel which formed the lower parallel surface 12 of the radiative heat switch also had an emissivity factor of approximately 0.92.

The hot and cold plates and the glass slab constitute the key components of the Northrup thermal conductivity apparatus which is described at pages 62 and 63 in G. B. Wilkes textbook entitled Heat Insulation, published in 1950 by John Wiley and Sons. Using the Northrup method, a series of determinations were made of the effective thermal conductivity k, measured in B.t.u.- in./hr.-ft. -F., of the heat switch above described at various louver settings. The measurements were taken when the system was at equilibrium and the mean temperature was 100 F.:l F. The'results of these measurements are set forth in the graph appearing in FIGURE 4.v Various angles from 0 to are plotted along the horizontal axis of the graph, these angles representing the angle defined 'by the louver and the pathof heat flow, which is along lines perpendicular to the major parallel surfaces of the heat switch. Thus, where the measurement is made with the angle equal to 0, the ionvers are in a position shown in FIGURE 2 and when the angle is 90 the louvers are in the position shown in FIG- URE 3. Effective thermal conductivity values k are plotted along the vertical axis. The effective thermal conductivity consists predominantly of two components, the conductivity resulting from gas conduction and the conductivity resulting from thermal radiation. The portion of the graph falling below the dotted line indicates the amount of thermal conductivity in the heat switch which is accounted for by gas conduction. The difference between this value and the value determined by a point on the curved line which shows the effective thermal consseassz The radiative heat switch is particularly well adapted for use within an exterior wall member or roof member.

in dwelling units. In such a construction, for instance during a warm summer day, the panel could be adjusted to give a good insulating value, i.e. adjusted asillustrated in FIGURE 3, so as to minimize the amount of heat flow through the particular section of the roof or wall in which the heat switch is incorporated. In the summer, on a cool evening, the louvers would be switched to the position shown in FIGURE 2 in order to allow heat to more readily pass through the heat switch, thus utilizing the coolness outside of the house unit to assist in cooling the interior of the house. Of course,-in the winter, the procedure for regulating heat flow through the heat switch would be modified so as to take advantage of the heat provided by the sun during the daytime by switching the louvers to the poistion shown in FIGURE 2.

would be largest when heat transfer processes other than thermal radiation are kept to a minimum. Heat transfer processes involving infiltration of air and water vapor could be kept to a minimum by sealing the heat switch unit. Convection heat transfer, of course, will occur except in that instance when the panel is oriented horizontally with the warm surface on top. However, this effect may be minimized by keeping the total thickness of the heat switch at a minimum and/or partial evacuation of the air from the interior of the sealed heat switch. In addition, heat transfer due to gaseous conduction can be lowered by replacing the air in a heat switch unit with a heavy gas, such as one of the Freons.

Any means, well known to those skilled in the art, could be provided for adjusting the louvers. Such means could be manual, mechanical, or electrical, orany com- During the evening hours, the louvers would be switched to the position shown in FIGURE 3 so as to provide a good insulating value and thus minmize heat flow from the heated house.

The degree of switching which may be accomplished with the heat switch of this invention is greatest when the two major surfaces 11 and 12 have a relatively high emissivity, preferably greater than about 0.9, and when the louvers It have a relatively low emissivity, preferably less than about 0.1.

The heat switch principle embodied in this invention may also be utilized in glass wall type buildingstructures.

Thus, the louver system may be incorporated into double glazed window units so as to permit variation in the effective thermal conductivity of the window units. ferring to'the drawings, in FIGURES 2 and '3, surfaces 11 and 12 would represent the window glass. When the louver system is used in combination with a double glazed window unit to provide a heat switch, the unit would preferably be sealed with water vapor excluded so as to prevent internal condensation. When used in window walls exposed directly to thesuns rays, the louvers would reflect ordinary sunlight, thus serving in addition the function ordinarily served by blinds ordrapes in reducingthe solar heating effect. The heat switch, of course, would permit variation in the effective thermal conductivity of the double glazed window unit and, when completely closed, the louver system in combination with the sealed double glazed window unit would act to sub stantially lower the minimum thermal conductivity below that of ordinary double. glazed window'units. 'In modern construction, the installation of this type of heat switch would allow for the use of smaller air conditioning units in large ofiice buildings and additionally, insofar as the louvers would be completely enclosed within the sealed double glazed window unit,'cleanin'g and maintenance would not be the problem encountered through the use of external means, such as Venetian blinds or drapes. V

The degree of switching effected by the heat switch bination of these. By way of example, manual means suchas those provided for opening and closing Venetian blinds could be used to open and close the heat switch or an electrical motor could be linked to each'louver by 'an appropriate arrangement of gears or other type of drive and the motor could be controlled locally or centrally as desired. Of course, when using an electrical motor, this motor may be placed within the panel or outside of the panel as conditions require. Also, where the outer parallel surfaces of the heat switch are formed of transparent materials, photoelectric controls could be used which would allow the sun to operate the louvers.

I claim:

1. A heat switch comprising in combination, a frame, two elements having emissivities to infrared radiation greater than about 0.9 and having substantially parallel surfaces enclosing said frame, and a series of louvers of high reflectivity to infrared radiation and having emis sivities to infrared radiation less than about 0.1 rotatably supported by said frame intermediate said parallel surfaces, said louvers, when in positions substantially parallel to said parallel surfaces, forming a substantially continuous reflective surface which defines two compartments in combination with the two parallel surfaces and theframe.

2. A heat switch comprising in combination, a frame, 0

two opaque elements having emissivities to infrared radiation greater than about 0.9 and having substantially parallel surfaces enclosing said frame, and a series of louvers of high reflectivity to infrared radiation and having emissivities to infrared radiation less than about 0.1 rotatably supported by said frame intermediate said parallel surfaces, said louvers, when in positions substantially parallel to said parallel surfaces, forming a substantially continuous reflective surface which defines two compartments in combination with the two parallel surfaces and the frame.

References Cited in the file of this patent UNITED STATES PATENTS 2,545,906 Watkins Mar. 20, 1951' 2,733,486 7 Peeples Feb. 7, 1956 2,857,634 Garbade et al. Oct. 28, 19 58 

1. A HEAT SWITCH COMPRISING IN COMBINATION, A FRAME, TWO ELEMENTS HAVING EMISSIVITIES TO INFRARED RADIATION GREATER THAN ABOUT 0.9 AND HAVING SUBSTANTIALLY PARALLEL SURFACES ENCLOSING SAID FRAME, AND A SERIES OF LOUVERS OF HIGH REFLECTIVITY TO INFRARED RADIATION AND HAVING EMISSIVITIES TO INFRARED RADIATIONS LESS THAN ABOUT 0.1 ROTATABLY SUPPORTED BY SAID FRAME INTERMEDIATE SAID PARALLEL SURFACES, SAID LOUVERS, WHEN IN POSITIONS SUBSTANTIALLY PARALLEL TO SAID PARALLEL SURFACES, FORMING A SUBSTANTIALLY CONTINUOUS REFLECTIVE SURFACE WHICH DEFINES TWO COMPARTMENTS IN COMBINATION WITH THE TWO PARALLEL SURFACES AND THE FRAME. 